It has been well known in the art that a biological tissue afflicted by a tumor (for example, breast cancer and prostatic cancer) significantly hardens as the tumor grows as compared with healthy tissues. It is also known that in a region afflicted by such tumor a transverse ultrasound has an increased speed. Thus, there has been proposed a method of discerning a tumor-afflicted biological region by transmitting an ultrasound wave through the region and measuring the ultrasound shear rate of the domain. (See for example, Patent Document 1 listed below.)